Calculating slope 

Release 9.2
Last modified May 2, 2007 
Print all topics in : "Surface analysis" 
The Slope tool calculates the maximum rate of change between each cell and its neighbors, for example, the steepest downhill descent for the cell (the maximum change in elevation over the distance between the cell and its eight neighbors). Every cell in the output raster has a slope value. The lower the slope value, the flatter the terrain; the higher the slope value, the steeper the terrain. The output slope raster can be calculated as percent of slope or degree of slope.
Learn how to calculate slope using the Spatial Analyst toolbar
Learn how to calculate slope using the Slope tool
When the slope angle equals 45 degrees, the rise is equal to the run. Expressed as a percentage, the slope of this angle is 100 percent. As the slope approaches vertical (90 degrees), the percentage slope approaches infinity.
The Slope tool is most frequently run on an elevation dataset, as the following diagrams show. Steeper slopes are shaded red on the output slope raster. However, the function can also be used with other types of continuous data, such as population, to identify sharp changes in value.